Informational R. Pantos, Ed.
Internet-Draft Apple Inc.
Intended status: Informational W. May
Expires: March 24, 2017 Major League Baseball Advanced Media
September 20, 2016
HTTP Live Streamingdraft-pantos-http-live-streaming-20
Abstract
This document describes a protocol for transferring unbounded streams
of multimedia data. It specifies the data format of the files and
the actions to be taken by the server (sender) and the clients
(receivers) of the streams. It describes version 7 of this protocol.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 24, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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This document may not be modified, and derivative works of it may not
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It provides a flexible framework for media encryption. It can
efficiently offer multiple renditions of the same content, such as
audio translations. It offers compatibility with large-scale HTTP
caching infrastructure to support delivery to large audiences.
Since its first draft publication in 2009, HTTP Live Streaming has
been implemented and deployed by a wide array of content producers,
tools vendors, distributors, and device manufacturers.
The purpose of this document is to facilitate interoperability
between HTTP Live Streaming implementations by describing the media
transmission protocol. Using this protocol, a client can receive a
continuous stream of media from a server for concurrent presentation.
This document describes version 7 of the protocol.
2. Overview
A multimedia presentation is specified by a Uniform Resource
Identifier (URI) [RFC3986] to a Playlist.
A Playlist is either a Media Playlist or a Master Playlist. Both are
UTF-8 text files containing URIs and descriptive tags.
A Media Playlist contains a list of Media Segments, which when played
sequentially will play the multimedia presentation.
Here is an example of a Media Playlist:
#EXTM3U
#EXT-X-TARGETDURATION:10
#EXTINF:9.009,
http://media.example.com/first.ts
#EXTINF:9.009,
http://media.example.com/second.ts
#EXTINF:3.003,
http://media.example.com/third.ts
The first line is the format identifier tag #EXTM3U. The line
containing #EXT-X-TARGETDURATION says that all Media Segments will be
10 seconds long or less. Then three Media Segments are declared.
The first and second are 9.009 seconds long; the third is 3.003
seconds.
To play this Playlist, the client first downloads it and then
downloads and plays each Media Segment declared within it. The
client reloads the Playlist as described in this document to discover
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any added segments. Data SHOULD be carried over HTTP [RFC7230], but
in general a URI can specify any protocol that can reliably transfer
the specified resource on demand.
A more complex presentation can be described by a Master Playlist. A
Master Playlist provides a set of Variant Streams, each of which
describes a different version of the same content.
A Variant Stream includes a Media Playlist that specifies media
encoded at a particular bit rate, in a particular format, and at a
particular resolution for media containing video.
A Variant Stream can also specify a set of Renditions. Renditions
are alternate versions of the content, such as audio produced in
different languages or video recorded from different camera angles.
Clients should switch between different Variant Streams to adapt to
network conditions. Clients should choose Renditions based on user
preferences.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Media Segments
A Media Playlist contains a series of Media Segments which make up
the overall presentation. A Media Segment is specified by a URI and
optionally a byte range.
The duration of each Media Segment is indicated in the Media Playlist
by its EXTINF tag (Section 4.3.2.1).
Each segment in a Media Playlist has a unique integer Media Sequence
Number. The Media Sequence Number of the first segment in the Media
Playlist is either 0, or declared in the Playlist (Section 4.3.3.2).
The Media Sequence Number of every other segment is equal to the
Media Sequence Number of the segment that precedes it plus one.
Each Media Segment MUST carry the continuation of the encoded
bitstream from the end of the segment with the previous Media
Sequence Number, where values in a series such as timestamps and
Continuity Counters MUST continue uninterrupted. The only exceptions
are the first Media Segment ever to appear in a Media Playlist, and
Media Segments which are explicitly signaled as discontinuities
(Section 4.3.2.3). Unmarked media discontinuities can trigger
playback errors.
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Any Media Segment that contains video SHOULD include enough
information to initialize a video decoder and decode a continuous set
of frames that includes the final frame in the Segment, and ideally
all frames in the Segment. For example, any Media Segment containing
H.264 video SHOULD contain an IDR, ideally at the beginning of the
Segment.
3.1. Supported Media Segment Formats
All Media Segments MUST be in a format described in this section.
Transport of other media file formats is not defined.
Some media formats require a common sequence of bytes to initialize a
parser before a Media Segment can be parsed. This format-specific
sequence is called the Media Initialization Section. The Media
Initialization Section can be specified by an EXT-X-MAP
(Section 4.3.2.5) tag.
3.2. MPEG-2 Transport Streams
MPEG-2 Transport Streams are specified by [ISO_13818].
The Media Initialization Section of an MPEG-2 Transport Stream
Segment is a Program Association Table (PAT) followed by a Program
Map Table (PMT).
Transport Stream Segments MUST contain a single MPEG-2 Program;
playback of Multi-Program Transport Streams is not defined. Each
Transport Stream Segment MUST contain a PAT and a PMT, ideally at the
start of the Segment, or have an EXT-X-MAP (Section 4.3.2.5) tag
applied to it.
3.3. Fragmented MPEG-4
MPEG-4 Fragments are specified by the ISO Base Media File Format
[ISOBMFF]. Unlike regular MPEG-4 files which have a Movie Box
('moov') that contains sample tables and a Media Data Box ('mdat')
containing the corresponding samples, an MPEG-4 Fragment consists of
a Movie Fragment Box ('moof') containing a subset of the sample table
and a Media Data Box containing those samples. Use of MPEG-4
Fragments does require a Movie Box for initialization, but that Movie
Box contains only non-sample-specific information such as track and
sample descriptions.
A Fragmented MPEG-4 (fMP4) Segment is a "segment" as defined by
Section 3 of [ISOBMFF], including the constraints on Media Data Boxes
in Section 8.16 [ISOBMFF].
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The Media Initialization Section for an fMP4 Segment is an ISO Base
Media File that can initialize a parser for that Segment. It MUST
contain a File Type Box ('ftyp') containing a brand that is
compatible with 'iso6' or higher. The File Type Box MUST be followed
by a Movie Box. The Movie Box MUST contain a Track Box ('trak') for
every Track Fragment Box ('traf') in the fMP4 Segment, with matching
track_ID. Each Track Box SHOULD contain a sample table, but its
sample count MUST be zero. Movie Header Boxes ('mvhd') and Track
Header Boxes ('tkhd') MUST have durations of zero. A Movie Extends
Box ('mvex') MUST follow the last Track Box.
In an fMP4 Segment, every Track Fragment Box MUST contain a Track
Fragment Decode Time Box ('tfdt'). fMP4 Segments MUST use movie-
fragment relative addressing. fMP4 Segments MUST NOT use external
data references.
An fMP4 Segment in a Playlist containing the EXT-X-I-FRAMES-ONLY
(Section 4.3.3.6) tag MAY omit the portion of the Media Data Box
following the I-frame sample data.
Each fMP4 Segment in a Media Playlist MUST have an EXT-X-MAP tag
applied to it.
3.4. Packed Audio
A Packed Audio Segment contains encoded audio samples and ID3 tags
that are simply packed together with minimal framing and no per-
sample timestamps. Supported Packed Audio formats are AAC with ADTS
framing [ISO_13818_7]; MP3 [ISO_13818_3]; AC-3 [AC_3]; and Enhanced
AC-3 [AC_3].
A Packed Audio Segment has no Media Initialization Section.
Each Packed Audio Segment MUST signal the timestamp of its first
sample with an ID3 PRIV tag [ID3] at the beginning of the segment.
The ID3 PRIV owner identifier MUST be
"com.apple.streaming.transportStreamTimestamp". The ID3 payload MUST
be a 33-bit MPEG-2 Program Elementary Stream timestamp expressed as a
big-endian eight-octet number, with the upper 31 bits set to zero.
Clients SHOULD NOT play Packed Audio Segments without this ID3 tag.
3.5. WebVTT
A WebVTT Segment is a section of a WebVTT [WebVTT] file. WebVTT
Segments carry subtitles.
The Media Initialization Section of a WebVTT Segment is the WebVTT
header.
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Each WebVTT Segment MUST contain all subtitle cues that are intended
to be displayed during the period indicated by the segment EXTINF
duration. The start time offset and end time offset of each cue MUST
indicate the total display time for that cue, even if part of the cue
time range is outside the Segment period. A WebVTT Segment MAY
contain no cues; this indicates that no subtitles are to be displayed
during that period.
Each WebVTT Segment MUST either start with a WebVTT header or have an
EXT-X-MAP tag applied to it.
In order to synchronize timestamps between audio/video and subtitles,
a X-TIMESTAMP-MAP metadata header SHOULD be added to each WebVTT
header. This header maps WebVTT cue timestamps to MPEG-2 (PES)
timestamps in other Renditions of the Variant Stream. Its format is:
X-TIMESTAMP-MAP=LOCAL:<cue time>,MPEGTS:<MPEG-2 time>
e.g. X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The cue timestamp in the LOCAL attribute MAY fall outside the range
of time covered by the segment.
If a WebVTT segment does not have the X-TIMESTAMP-MAP, the client
MUST assume that the WebVTT cue time of 0 maps to an MPEG-2 timestamp
of 0.
4. Playlists
This section describes the Playlist files used by HTTP Live
Streaming. In this section, "MUST" and "MUST NOT" specify the rules
for the syntax and structure of legal Playlist files. Playlists that
violate these rules are invalid; clients MUST fail to parse them.
See Section 6.3.2.
The format of the Playlist files is derived from the M3U [M3U]
playlist file format and inherits two tags from that earlier file
format: EXTM3U (Section 4.3.1.1) and EXTINF (Section 4.3.2.1).
In this section, tags are specified using a BNF-style syntax.
Each Playlist file MUST be identifiable by either the path component
of its URI or by HTTP Content-Type. In the first case, the path MUST
end with either .m3u8 or .m3u. In the second, the HTTP Content-type
MUST be "application/vnd.apple.mpegurl" or "audio/mpegurl". Clients
SHOULD refuse to parse Playlists that are not so identified.
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Playlist files MUST be encoded in UTF-8 [RFC3629]. They MUST NOT
contain any byte order mark (BOM); Clients SHOULD reject Playlists
which contain a BOM or do not parse as UTF-8. Playlist files MUST
NOT contain UTF-8 control characters (U+0000 to U+001F and U+007F to
U+009F), with the exceptions of CR (U+000D) and LF (U+000A). All
character sequences MUST be normalized according to Unicode
normalization form "NFC". Note that US-ASCII [US_ASCII] conforms to
these rules.
Lines in a Playlist file are terminated by either a single line feed
character or a carriage return character followed by an line feed
character. Each line is a URI, blank, or starts with the character
'#'. Blank lines are ignored. White space MUST NOT be present,
except for elements in which it is explicitly specified.
Lines that start with the character '#' are either comments or tags.
Tags begin with #EXT. They are case-sensitive. All other lines that
begin with '#' are comments and SHOULD be ignored.
A URI line identifies a Media Segment or a Playlist file (see
Section 4.3.4.2). Each Media Segment is specified by a URI and the
tags that apply to it.
A Playlist is a Media Playlist if all URI lines in the Playlist
identify Media Segments. A Playlist is a Master Playlist if all URI
lines in the Playlist identify Media Playlists. A Playlist MUST be
either a Media Playlist or a Master Playlist; all other Playlists are
invalid.
A URI in a Playlist, whether it is a URI line or part of a tag, MAY
be relative. Any relative URI is considered to be relative to the
URI of the Playlist that contains it.
The duration of a Media Playlist file is the sum of the durations of
the Media Segments within it.
The segment bit rate of a Media Segment is the size of the Media
Segment divided by its EXTINF duration (Section 4.3.2.1). Note that
this includes container overhead but does not include overhead
imposed by the delivery system, such as HTTP, TCP or IP headers.
The peak segment bit rate of a Media Playlist is the largest bit rate
of any contiguous set of segments whose total duration is between 0.5
and 1.5 times the target duration. The bit rate of a set is
calculated by dividing the sum of the segment sizes by the sum of the
segment durations.
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The average segment bit rate of a Media Playlist is the sum of the
sizes (in bits) of every Media Segment in the Media Playlist, divided
by the Media Playlist duration. Note that this includes container
overhead, but not HTTP or other overhead imposed by the delivery
system.
4.2. Attribute Lists
Certain tags have values which are Attribute Lists. An Attribute
List is a comma-separated list of attribute/value pairs with no
whitespace.
An attribute/value pair has the following syntax:
AttributeName=AttributeValue
An AttributeName is an unquoted string containing characters from the
set [A..Z], [0..9] and '-'. Therefore, AttributeNames contain only
uppercase letters, not lowercase. There MUST NOT be any whitespace
between the AttributeName and the '=' character, nor between the '='
character and the AttributeValue.
An AttributeValue is one of the following:
o decimal-integer: an unquoted string of characters from the set
[0..9] expressing an integer in base-10 arithmetic in the range
from 0 to 2^64-1 (18446744073709551615). A decimal-integer may be
from 1 to 20 characters long.
o hexadecimal-sequence: an unquoted string of characters from the
set [0..9] and [A..F] that is prefixed with 0x or 0X. The maximum
length of a hexadecimal-sequence depends on its AttributeName.
o decimal-floating-point: an unquoted string of characters from the
set [0..9] and '.' which expresses a non-negative floating-point
number in decimal positional notation.
o signed-decimal-floating-point: an unquoted string of characters
from the set [0..9], '-' and '.' which expresses a signed
floating-point number in decimal positional notation.
o quoted-string: a string of characters within a pair of double-
quotes (0x22). The following characters MUST NOT appear in a
quoted-string: line feed (0xA), carriage return (0xD), or double
quote (0x22). Quoted-string AttributeValues SHOULD be constructed
so that byte-wise comparison is sufficient to test two quoted-
string AttributeValues for equality. Note that this implies case-
sensitive comparison.
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o enumerated-string: an unquoted character string from a set which
is explicitly defined by the Attribute. An enumerated-string will
never contain double-quotes ("), commas (,), or whitespace.
o decimal-resolution: two decimal-integers separated by the "x"
character. The first integer is a horizontal pixel dimension
(width); the second is a vertical pixel dimension (height).
The type of the AttributeValue for a given AttributeName is specified
by the Attribute definition.
A given AttributeName MUST NOT appear more than once in a given
Attribute List. Clients SHOULD refuse to play such Playlists.
4.3. Playlist Tags
Playlist tags specify either global parameters of the Playlist, or
information about the Media Segments or Media Playlists that appear
after them.
4.3.1. Basic Tags
These tags are allowed in both Media Playlists and Master Playlists.
4.3.1.1. EXTM3U
The EXTM3U tag indicates that the file is an Extended M3U [M3U]
Playlist file. It MUST be the first line of every Media Playlist and
every Master Playlist. Its format is:
#EXTM3U
4.3.1.2. EXT-X-VERSION
The EXT-X-VERSION tag indicates the compatibility version of the
Playlist file, its associated media, and its server.
The EXT-X-VERSION tag applies to the entire Playlist file. Its
format is:
#EXT-X-VERSION:<n>
where n is an integer indicating the protocol compatibility version
number.
It MUST appear in all Playlists containing tags or attributes that
are not compatible with protocol version 1 to support
interoperability with older clients. Section 7 specifies the minimum
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value of the compatibility version number for any given Playlist
file.
A Playlist file MUST NOT contain more than one EXT-X-VERSION tag. If
a client encounters a Playlist with multiple EXT-X-VERSION tags, it
MUST reject it.
4.3.2. Media Segment Tags
Each Media Segment is specified by a series of Media Segment tags
followed by a URI. Some Media Segment tags apply to just the next
segment; others apply to all subsequent segments until another
instance of the same tag.
A Media Segment tag MUST NOT appear in a Master Playlist. Clients
MUST reject Playlists that contain both Media Segment Tags and Master
Playlist tags (Section 4.3.4).
4.3.2.1. EXTINF
The EXTINF tag specifies the duration of a Media Segment. It applies
only to the next Media Segment. This tag is REQUIRED for each Media
Segment. Its format is:
#EXTINF:<duration>,[<title>]
where duration is a decimal-floating-point or decimal-integer number
(as described in Section 4.2) that specifies the duration of the
Media Segment in seconds. Generally, durations SHOULD be decimal-
floating-point, with enough accuracy to avoid perceptible error when
segment durations are accumulated. If the compatibility version
number is less than 3, durations MUST be integers. Durations that
are reported as integers SHOULD be rounded to the nearest integer.
The remainder of the line following the comma is an optional human-
readable informative title of the Media Segment expressed as raw
UTF-8 text.
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The EXT-X-BYTERANGE tag indicates that a Media Segment is a sub-range
of the resource identified by its URI. It applies only to the next
URI line that follows it in the Playlist. Its format is:
#EXT-X-BYTERANGE:<n>[@<o>]
where n is a decimal-integer indicating the length of the sub-range
in bytes. If present, o is a decimal-integer indicating the start of
the sub-range, as a byte offset from the beginning of the resource.
If o is not present, the sub-range begins at the next byte following
the sub-range of the previous Media Segment.
If o is not present, a previous Media Segment MUST appear in the
Playlist file and MUST be a sub-range of the same media resource, or
the Media Segment is undefined and the Playlist MUST be rejected.
A Media Segment without an EXT-X-BYTERANGE tag consists of the entire
resource identified by its URI.
Use of the EXT-X-BYTERANGE tag REQUIRES a compatibility version
number of 4 or greater.
4.3.2.3. EXT-X-DISCONTINUITY
The EXT-X-DISCONTINUITY tag indicates a discontinuity between the
Media Segment that follows it and the one that preceded it.
Its format is:
#EXT-X-DISCONTINUITY
The EXT-X-DISCONTINUITY tag MUST be present if there is a change in
any of the following characteristics:
o file format
o number, type and identifiers of tracks
o timestamp sequence
The EXT-X-DISCONTINUITY tag SHOULD be present if there is a change in
any of the following characteristics:
o encoding parameters
o encoding sequence
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See Section 3, Section 6.2.1, and Section 6.3.3 for more information
about the EXT-X-DISCONTINUITY tag.
4.3.2.4. EXT-X-KEY
Media Segments MAY be encrypted. The EXT-X-KEY tag specifies how to
decrypt them. It applies to every Media Segment that appears between
it and the next EXT-X-KEY tag in the Playlist file with the same
KEYFORMAT attribute (or the end of the Playlist file). Two or more
EXT-X-KEY tags with different KEYFORMAT attributes MAY apply to the
same Media Segment if they ultimately produce the same decryption
key. The format is:
#EXT-X-KEY:<attribute-list>
The following attributes are defined:
METHOD
The value is an enumerated-string that specifies the encryption
method. This attribute is REQUIRED.
The methods defined are: NONE, AES-128, and SAMPLE-AES.
An encryption method of NONE means that Media Segments are not
encrypted. If the encryption method is NONE, other attributes
MUST NOT be present.
An encryption method of AES-128 signals that Media Segments are
completely encrypted using the Advanced Encryption Standard
[AES_128] with a 128-bit key, Cipher Block Chaining, and PKCS7
padding [RFC5652]. CBC is restarted on each segment boundary,
using either the IV attribute value or the Media Sequence Number
as the IV; see Section 5.2.
An encryption method of SAMPLE-AES means that the Media Segments
contain media samples, such as audio or video, that are encrypted
using the Advanced Encryption Standard [AES_128]. How these media
streams are encrypted and encapsulated in a segment depends on the
media encoding and the media format of the segment. fMP4 Media
Segments are encrypted using the 'cbcs' scheme of Common
Encryption [COMMON_ENC]. Encryption of other Media Segment
formats containing H.264 [H_264], AAC [ISO_14496], AC-3 [AC_3],
and Enhanced AC-3 [AC_3] media streams is described in the HLS
Sample Encryption [SampleEnc] specification. The IV attribute MAY
be present; see Section 5.2.
URI
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The value is a quoted-string containing a URI that specifies how
to obtain the key. This attribute is REQUIRED unless the METHOD
is NONE.
IV
The value is a hexadecimal-sequence that specifies a 128-bit
unsigned integer Initialization Vector to be used with the key.
Use of the IV attribute REQUIRES a compatibility version number of
2 or greater. See Section 5.2 for when the IV attribute is used.
KEYFORMAT
The value is a quoted-string that specifies how the key is
represented in the resource identified by the URI; see Section 5
for more detail. This attribute is OPTIONAL; its absence
indicates an implicit value of "identity". Use of the KEYFORMAT
attribute REQUIRES a compatibility version number of 5 or greater.
KEYFORMATVERSIONS
The value is a quoted-string containing one or more positive
integers separated by the "/" character (for example, "1", "1/2",
or "1/2/5"). If more than one version of a particular KEYFORMAT
is defined, this attribute can be used to indicate which
version(s) this instance complies with. This attribute is
OPTIONAL; if it is not present, its value is considered to be "1".
Use of the KEYFORMATVERSIONS attribute REQUIRES a compatibility
version number of 5 or greater.
If the Media Playlist file does not contain an EXT-X-KEY tag then
Media Segments are not encrypted.
See Section 5 for the format of the key file, and Section 5.2,
Section 6.2.3 and Section 6.3.6 for additional information on Media
Segment encryption.
4.3.2.5. EXT-X-MAP
The EXT-X-MAP tag specifies how to obtain the Media Initialization
Section (Section 3) required to parse the applicable Media Segments.
It applies to every Media Segment that appears after it in the
Playlist until the next EXT-X-MAP tag or until the end of the
playlist.
Its format is:
#EXT-X-MAP:<attribute-list>
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The following attributes are defined:
URI
The value is a quoted-string containing a URI that identifies a
resource that contains the Media Initialization Section. This
attribute is REQUIRED.
BYTERANGE
The value is a quoted-string specifying a byte range into the
resource identified by the URI attribute. This range SHOULD
contain only the Media Initialization Section. The format of the
byte range is described in Section 4.3.2.2. This attribute is
OPTIONAL; if it is not present, the byte range is the entire
resource indicated by the URI.
An EXT-X-MAP tag SHOULD be supplied for Media Segments in Playlists
with the EXT-X-I-FRAMES-ONLY tag when the first Media Segment (i.e.,
I-frame) in the Playlist (or the first segment following an
EXT-X-DISCONTINUITY tag) does not immediately follow the Media
Initialization Section at the beginning of its resource.
Use of the EXT-X-MAP tag in a Media Playlist that contains the
EXT-X-I-FRAMES-ONLY tag REQUIRES a compatibility version number of 5
or greater. Use of the EXT-X-MAP tag in a Media Playlist that DOES
NOT contain the EXT-X-I-FRAMES-ONLY tag REQUIRES a compatibility
version number of 6 or greater.
4.3.2.6. EXT-X-PROGRAM-DATE-TIME
The EXT-X-PROGRAM-DATE-TIME tag associates the first sample of a
Media Segment with an absolute date and/or time. It applies only to
the next Media Segment.
The date/time representation is ISO/IEC 8601:2004 [ISO_8601] and
SHOULD indicate a time zone and fractional parts of seconds:
#EXT-X-PROGRAM-DATE-TIME:<YYYY-MM-DDThh:mm:ss.SSSZ>
For example:
#EXT-X-PROGRAM-DATE-TIME:2010-02-19T14:54:23.031+08:00
EXT-X-PROGRAM-DATE-TIME tags SHOULD provide millisecond accuracy.
See Section 6.2.1 and Section 6.3.3 for more information on the EXT-X
-PROGRAM-DATE-TIME tag.
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The EXT-X-DATERANGE tag associates a Date Range (i.e. a range of time
defined by a starting and ending date) with a set of attribute /
value pairs. Its format is:
#EXT-X-DATERANGE:<attribute-list>
where the defined attributes are:
ID
A quoted-string that uniquely identifies a Date Range in the
Playlist. This attribute is REQUIRED.
CLASS
A client-defined quoted-string that specifies some set of
attributes and their associated value semantics. All Date Ranges
with the same CLASS attribute value MUST adhere to these
attribute-value semantics. This attribute is OPTIONAL.
START-DATE
A quoted-string containing the ISO-8601 date at which the Date
Range begins. This attribute is REQUIRED.
END-DATE
A quoted-string containing the ISO-8601 date at which the Date
Range ends. It MUST be equal to or later than the value of the
START-DATE attribute. This attribute is OPTIONAL.
DURATION
The duration of the Date Range expressed as a decimal-floating-
point number of seconds. It MUST NOT be negative. A single
instant in time (e.g. crossing a finish line) SHOULD be
represented with a duration of 0. This attribute is OPTIONAL.
PLANNED-DURATION
The expected duration of the Date Range expressed as a decimal-
floating-point number of seconds. It MUST NOT be negative. This
attribute SHOULD be used to indicate the expected duration of a
Date Range whose actual duration is not yet known. It is
OPTIONAL.
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X-<client-attribute>
The "X-" prefix defines a namespace reserved for client-defined
attributes. The client-attribute MUST be a legal AttributeName.
Clients SHOULD use a reverse-DNS syntax when defining their own
attribute names to avoid collisions. The attribute value MUST be
a quoted-string, a hexadecimal-sequence, or a decimal-floating-
point. An example of a client-defined attribute is X-COM-EXAMPLE-
AD-ID="XYZ123". These attributes are OPTIONAL.
SCTE35-CMD, SCTE35-OUT, SCTE35-IN
Used to carry SCTE-35 data; see Section 4.3.2.7.1 for more
information. These attributes are OPTIONAL.
END-ON-NEXT
An enumerated-string whose value MUST be YES. This attribute
indicates that the end of the range containing it is equal to the
START-DATE of its Following Range. The Following Range is the
Date Range of the same CLASS that has the earliest START-DATE
after the START-DATE of the range in question. This attribute is
OPTIONAL.
An EXT-X-DATERANGE tag with an END-ON-NEXT=YES attribute MUST have a
CLASS attribute. Other EXT-X-DATERANGE tags with the same CLASS
attribute MUST NOT specify Date Ranges that overlap.
An EXT-X-DATERANGE tag with an END-ON-NEXT=YES attribute MUST NOT
contain DURATION or END-DATE attributes.
A Date Range with neither a DURATION, an END-DATE, or an END-ON-
NEXT=YES attribute has an unknown duration, even if it has a PLANNED-
DURATION.
If a Playlist contains an EXT-X-DATERANGE tag, it MUST also contain
at least one EXT-X-PROGRAM-DATE-TIME tag.
If a Playlist contains two EXT-X-DATERANGE tags with the same ID
attribute value, then any AttributeName that appears in both tags
MUST have the same AttributeValue.
If a Date Range contains both a DURATION attribute and an END-DATE
attribute, the value of the END-DATE attribute MUST be equal to the
value of the START-DATE attribute plus the value of the DURATION
attribute.
Clients SHOULD ignore EXT-X-DATERANGE tags with illegal syntax.
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Splice information carried in source media according to the SCTE-35
specification [SCTE35] MAY be represented in a Media Playlist using
EXT-X-DATERANGE tags.
Each SCTE-35 splice_info_section() containing a splice_null(),
splice_schedule(), bandwidth_reservation() or private_cmd() SHOULD be
represented by an EXT-X-DATERANGE tag with a SCTE35-CMD attribute
whose value is the big-endian binary representation of the
splice_info_section(), expressed as a hexadecimal-sequence.
A SCTE-35 splice out/in pair signaled by a pair of splice_insert()
commands SHOULD be represented by one or more EXT-X-DATERANGE tags
carrying the same ID attribute, which MUST be unique to that splice
out/in pair. The "out" splice_info_section() (with
out_of_network_indicator set to 1) MUST be placed in a SCTE35-OUT
attribute, with the same formatting as SCTE35-CMD. The "in"
splice_info_section() (with out_of_network_indicator set to 0) MUST
be placed in a SCTE35-IN attribute, with the same formatting as
SCTE35-CMD.
A SCTE-35 splice out/in pair signaled by a pair of time_signal()
commands, each carrying a single segmentation_descriptor(), SHOULD be
represented by one or more EXT-X-DATERANGE tags carrying the same ID
attribute, which MUST be unique to that splice out/in pair. The
"out" splice_info_section() MUST be placed in a SCTE35-OUT attribute;
the "in" splice_info_section() MUST be placed in a SCTE35-IN
attribute.
Different types of segmentation (as indicated by the
segmentation_type_id in the segmentation_descriptor() SHOULD be
represented by separate EXT-X-DATERANGE tags, even if two or more
segmentation_descriptor()s arrive in the same splice_info_section().
In that case, each EXT-X-DATERANGE tag will have a SCTE35-OUT,
SCTE35-IN or SCTE35-CMD attribute whose value is the entire
splice_info_section().
A SCTE-35 time_signal() command that does not signal a splice out or
in point SHOULD be represented by an EXT-X-DATERANGE tag with a
SCTE35-CMD attribute.
The START-DATE of an EXT-X-DATERANGE tag containing a SCTE35-OUT
attribute MUST be the date and time that corresponds to the program
time of that splice.
The START-DATE of an EXT-X-DATERANGE tag containing a SCTE35-CMD MUST
be the date and time specified by the splice_time() in the command,
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or to the program time at which the command appeared in the source
stream if the command does not specify a splice_time().
An EXT-X-DATERANGE tag containing a SCTE35-OUT attribute MAY contain
a PLANNED-DURATION attribute. Its value MUST be the planned duration
of the splice.
The DURATION of an EXT-X-DATERANGE tag containing a SCTE35-IN
attribute MUST be the actual (not planned) program duration between
the corresponding out-point and that in-point.
The END-DATE of an EXT-X-DATERANGE tag containing a SCTE35-IN
attribute MUST be the actual (not planned) program date and time of
that in-point.
If the actual end date and time is not known when a SCTE35-OUT
attribute is added to the Playlist, the DURATION attribute and the
END-TIME attribute MUST NOT be present; the actual end date of the
splice SHOULD be signaled by another EXT-X-DATERANGE tag once it has
been established.
A canceled splice SHOULD NOT appear in the Playlist as an
EXT-X-DATERANGE tag.
An EXT-X-DATERANGE tag announcing a splice SHOULD be added to a
Playlist at the same time as the last pre-splice Media Segment.
The ID attribute of an EXT-X-DATERANGE tag MAY contain a
splice_event_id and/or a segmentation_event_id, but it MUST be unique
in the the Playlist. If there is a possibility that a SCTE-35 id
will be reused, the ID attribute value MUST include disambiguation,
such as a date or sequence number.
4.3.3. Media Playlist Tags
Media Playlist tags describe global parameters of the Media Playlist.
There MUST NOT be more than one Media Playlist tag of each type in
any Media Playlist.
A Media Playlist Tag MUST NOT appear in a Master Playlist
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The EXT-X-TARGETDURATION tag specifies the maximum Media Segment
duration. The EXTINF duration of each Media Segment in the Playlist
file, when rounded to the nearest integer, MUST be less than or equal
to the target duration; longer segments can trigger playback stalls
or other errors. It applies to the entire Playlist file. Its format
is:
#EXT-X-TARGETDURATION:<s>
where s is a decimal-integer indicating the target duration in
seconds. The EXT-X-TARGETDURATION tag is REQUIRED.
4.3.3.2. EXT-X-MEDIA-SEQUENCE
The EXT-X-MEDIA-SEQUENCE tag indicates the Media Sequence Number of
the first Media Segment that appears in a Playlist file. Its format
is:
#EXT-X-MEDIA-SEQUENCE:<number>
where number is a decimal-integer.
If the Media Playlist file does not contain an EXT-X-MEDIA-SEQUENCE
tag then the Media Sequence Number of the first Media Segment in the
Media Playlist SHALL be considered to be 0. A client MUST NOT assume
that segments with the same Media Sequence Number in different Media
Playlists contain matching content - see Section 6.3.2.
A URI for a Media Segment is not required to contain its Media
Sequence Number.
See Section 6.2.1 and Section 6.3.5 for more information on setting
the EXT-X-MEDIA-SEQUENCE tag.
The EXT-X-MEDIA-SEQUENCE tag MUST appear before the first Media
Segment in the Playlist.
4.3.3.3. EXT-X-DISCONTINUITY-SEQUENCE
The EXT-X-DISCONTINUITY-SEQUENCE tag allows synchronization between
different Renditions of the same Variant Stream or different Variant
Streams that have EXT-X-DISCONTINUITY tags in their Media Playlists.
Its format is:
#EXT-X-DISCONTINUITY-SEQUENCE:<number>
where number is a decimal-integer.
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If the Media Playlist does not contain an EXT-X-DISCONTINUITY-
SEQUENCE tag, then the Discontinuity Sequence Number of the first
Media Segment in the Playlist SHALL be considered to be 0.
The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before the first
Media Segment in the Playlist.
The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before any
EXT-X-DISCONTINUITY tag.
See Section 6.2.1 and Section 6.2.2 for more information about
setting the value of the EXT-X-DISCONTINUITY-SEQUENCE tag.
4.3.3.4. EXT-X-ENDLIST
The EXT-X-ENDLIST tag indicates that no more Media Segments will be
added to the Media Playlist file. It MAY occur anywhere in the Media
Playlist file. Its format is:
#EXT-X-ENDLIST
4.3.3.5. EXT-X-PLAYLIST-TYPE
The EXT-X-PLAYLIST-TYPE tag provides mutability information about the
Media Playlist file. It applies to the entire Media Playlist file.
It is OPTIONAL. Its format is:
#EXT-X-PLAYLIST-TYPE:<EVENT|VOD>
Section 6.2.1 defines the implications of the EXT-X-PLAYLIST-TYPE
tag.
If the EXT-X-PLAYLIST-TYPE value is EVENT, Media Segments can only be
added to the end of the Media Playlist. If the EXT-X-PLAYLIST-TYPE
value is VOD, the Media Playlist cannot change.
If the EXT-X-PLAYLIST-TYPE tag is omitted from a Media Playlist, the
Playlist can be updated according to the rules in Section 6.2.1 with
no additional restrictions. For example, a live Playlist
(Section 6.2.2) MAY be updated to remove Media Segments in the order
that they appeared.
4.3.3.6. EXT-X-I-FRAMES-ONLY
The EXT-X-I-FRAMES-ONLY tag indicates that each Media Segment in the
Playlist describes a single I-frame. I-frames (or Intra frames) are
encoded video frames whose encoding does not depend on any other
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frame. I-frame playlists can be used for trick play, such as fast
forward, rapid reverse and scrubbing.
The EXT-X-I-FRAMES-ONLY tag applies to the entire Playlist. Its
format is:
#EXT-X-I-FRAMES-ONLY
In a Playlist with the EXT-X-I-FRAMES-ONLY tag, the Media Segment
duration (EXTINF tag value) is the time between the presentation time
of the I-frame in the Media Segment and the presentation time of the
next I-frame in the Playlist, or the end of the presentation if it is
the last I-frame in the Playlist.
Media resources containing I-frame segments MUST begin with either a
Media Initialization Section (Section 3) or be accompanied by an
EXT-X-MAP tag indicating the Media Initialization Section so that
clients can load and decode I-frame segments in any order. The byte
range of an I-frame segment with an EXT-X-BYTERANGE tag applied to it
(Section 4.3.2.2) MUST NOT include its Media Initialization Section;
clients can assume that the Media Initialization Section is defined
by EXT-X-MAP tag, or is located from the start of the resource to the
offset of the first I-frame segment in that resource.
Use of the EXT-X-I-FRAMES-ONLY REQUIRES a compatibility version
number of 4 or greater.
4.3.4. Master Playlist Tags
Master Playlist tags define the Variant Streams, Renditions, and
other global parameters of the presentation.
Master Playlist Tags MUST NOT appear in a Media Playlist; clients
MUST reject any Playlist that contains both a Master Playlist tag and
either a Media Playlist tag or a Media Segment tag.
4.3.4.1. EXT-X-MEDIA
The EXT-X-MEDIA tag is used to relate Media Playlists that contain
alternative Renditions (Section 4.3.4.2.1) of the same content. For
example, three EXT-X-MEDIA tags can be used to identify audio-only
Media Playlists that contain English, French and Spanish Renditions
of the same presentation. Or two EXT-X-MEDIA tags can be used to
identify video-only Media Playlists that show two different camera
angles.
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Its format is:
#EXT-X-MEDIA:<attribute-list>
The following attributes are defined:
TYPE
The value is an enumerated-string; valid strings are AUDIO, VIDEO,
SUBTITLES and CLOSED-CAPTIONS. This attribute is REQUIRED.
In Transport Streams, Closed captions [CEA608] media is carried in
the video stream. Therefore, an EXT-X-MEDIA tag with TYPE of
CLOSED-CAPTION does not specify a Rendition; the closed caption
media is present in the Media Segments of every video Rendition.
URI
The value is a quoted-string containing a URI that identifies the
Media Playlist file. This attribute is OPTIONAL; see
Section 4.3.4.2.1. If the TYPE is CLOSED-CAPTIONS, the URI
attribute MUST NOT be present.
GROUP-ID
The value is a quoted-string which specifies the group to which
the Rendition belongs. See Section 4.3.4.1.1. This attribute is
REQUIRED.
LANGUAGE
The value is a quoted-string containing one of the standard Tags
for Identifying Languages [RFC5646], which identifies the primary
language used in the Rendition. This attribute is OPTIONAL.
ASSOC-LANGUAGE
The value is a quoted-string containing a language tag [RFC5646]
that identifies a language that is associated with the Rendition.
An associated language is often used in a different role than the
language specified by the LANGUAGE attribute (e.g. written vs.
spoken, or as a fallback dialect). This attribute is OPTIONAL.
The LANGUAGE and ASSOC-LANGUAGE attributes can be used, for
example, to link Norwegian renditions that use different spoken
and written languages.
NAME
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The value is a quoted-string containing a human-readable
description of the Rendition. If the LANGUAGE attribute is
present then this description SHOULD be in that language. This
attribute is REQUIRED.
DEFAULT
The value is an enumerated-string; valid strings are YES and NO.
If the value is YES, then the client SHOULD play this Rendition of
the content in the absence of information from the user indicating
a different choice. This attribute is OPTIONAL. Its absence
indicates an implicit value of NO.
AUTOSELECT
The value is an enumerated-string; valid strings are YES and NO.
This attribute is OPTIONAL. Its absence indicates an implicit
value of NO. If the value is YES, then the client MAY choose to
play this Rendition in the absence of explicit user preference
because it matches the current playback environment, such as
chosen system language.
If the AUTOSELECT attribute is present, its value MUST be YES if
the value of the DEFAULT attribute is YES.
FORCED
The value is an enumerated-string; valid strings are YES and NO.
This attribute is OPTIONAL. Its absence indicates an implicit
value of NO. The FORCED attribute MUST NOT be present unless the
TYPE is SUBTITLES.
A value of YES indicates that the Rendition contains content which
is considered essential to play. When selecting a FORCED
Rendition, a client SHOULD choose the one that best matches the
current playback environment (e.g. language).
A value of NO indicates that the Rendition contains content which
is intended to be played in response to explicit user request.
INSTREAM-ID
The value is a quoted-string that specifies a Rendition within the
segments in the Media Playlist. This attribute is REQUIRED if the
TYPE attribute is CLOSED-CAPTIONS, in which case it MUST have one
of the values: "CC1", "CC2", "CC3", "CC4", or "SERVICEn" where n
MUST be an integer between 1 and 63 (e.g."SERVICE3" or
"SERVICE42").
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The values "CC1", "CC2", "CC3", and "CC4" identify a Line 21 Data
Services channel [CEA608]. The "SERVICE" values identify a
Digital Television Closed Captioning [CEA708] service block
number.
For all other TYPE values, the INSTREAM-ID MUST NOT be specified.
CHARACTERISTICS
The value is a quoted-string containing one or more Uniform Type
Identifiers [UTI] separated by comma (,) characters. This
attribute is OPTIONAL. Each UTI indicates an individual
characteristic of the Rendition.
A SUBTITLES Rendition MAY include the following characteristics:
"public.accessibility.transcribes-spoken-dialog";
"public.accessibility.describes-music-and-sound"; "public.easy-to-
read" (which indicates that the subtitles have been edited for
ease of reading).
An AUDIO Rendition MAY include the following characteristics:
"public.accessibility.describes-video".
The CHARACTERISTICS attribute MAY include private UTIs.
CHANNELS
The value is a quoted-string that specifies an ordered,
"/"-separated list of parameters. If the TYPE attribute is AUDIO
then the first parameter is the count of independent audio
channels expressed as a decimal-integer. For example, an AC-3 5.1
rendition would have a CHANNELS="6" attribute. No other
parameters are currently defined.
All audio EXT-X-MEDIA tags SHOULD have a CHANNELS attribute. If a
Master Playlist contains two renditions encoded with the same
codec but a different number of channels, then the CHANNEL
attribute is REQUIRED; otherwise it is OPTIONAL.
4.3.4.1.1. Rendition Groups
A set of one or more EXT-X-MEDIA tags with the same GROUP-ID value
and the same TYPE value defines a Group of Renditions. Each member
of the Group MUST be an alternative rendition of the same content;
otherwise playback errors can occur.
All EXT-X-MEDIA tags in a Playlist MUST meet the following
constraints:
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o All EXT-X-MEDIA tags in the same Group MUST have different NAME
attributes.
o A Group MUST NOT have more than one member with a DEFAULT
attribute of YES.
o All members of a Group whose AUTOSELECT attribute has a value of
YES MUST have LANGUAGE [RFC5646] attributes with unique values.
A Playlist MAY contain multiple Groups of the same TYPE in order to
provide multiple encodings of that media type. If it does so, each
Group of the same TYPE MUST have the same set of members, and each
corresponding member MUST have identical attributes with the
exception of the URI attribute.
Each member in a Group of Renditions MAY have a different sample
format. However, any EXT-X-STREAM-INF (Section 4.3.4.2) tag or
EXT-X-I-FRAME-STREAM-INF (Section 4.3.4.3) tag which references that
Group MUST have a CODECS attribute that lists every sample format
present in any Rendition in the Group, or client playback failures
can occur.
4.3.4.2. EXT-X-STREAM-INF
The EXT-X-STREAM-INF tag specifies a Variant Stream, which is a set
of Renditions which can be combined to play the presentation. The
attributes of the tag provide information about the Variant Stream.
The URI line that follows the EXT-X-STREAM-INF tag specifies a Media
Playlist that carries a Rendition of the Variant Stream. The URI
line is REQUIRED. Clients that do not support multiple video
renditions SHOULD play this Rendition
Its format is:
#EXT-X-STREAM-INF:<attribute-list>
<URI>
The following attributes are defined:
BANDWIDTH
The value is a decimal-integer of bits per second. It represents
the peak segment bit rate of the Variant Stream.
If all the Media Segments in a Variant Stream have already been
created, the BANDWIDTH value MUST be the largest sum of peak
segment bit rates that is produced by any playable combination of
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Renditions. (For a Variant Stream with a single Media Playlist,
this is just the peak segment bit rate of that Media Playlist.)
An inaccurate value can cause playback stalls or prevent clients
from playing the variant.
If the Master Playlist is to be made available before all Media
Segments in the presentation have been encoded, the BANDWIDTH
value SHOULD be the BANDWIDTH value of a representative period of
similar content, encoded using the same settings.
Every EXT-X-STREAM-INF tag MUST include the BANDWIDTH attribute.
AVERAGE-BANDWIDTH
The value is a decimal-integer of bits per second. It represents
the average segment bit rate of the Variant Stream.
If all the Media Segments in a Variant Stream have already been
created, the AVERAGE-BANDWIDTH value MUST be the largest sum of
average segment bit rates that is produced by any playable
combination of Renditions. (For a Variant Stream with a single
Media Playlist, this is just the average segment bit rate of that
Media Playlist.) An inaccurate value can cause playback stalls or
prevent clients from playing the variant.
If the Master Playlist is to be made available before all Media
Segments in the presentation have been encoded, the AVERAGE-
BANDWIDTH value SHOULD be the AVERAGE-BANDWIDTH value of a
representative period of similar content, encoded using the same
settings.
The AVERAGE-BANDWIDTH attribute is OPTIONAL.
CODECS
The value is a quoted-string containing a comma-separated list of
formats, where each format specifies a media sample type that is
present in one or more Renditions specified by the Variant Stream.
Valid format identifiers are those in the ISO Base Media File
Format Name Space defined by The 'Codecs' and 'Profiles'
Parameters for "Bucket" Media Types [RFC6381].
For example, a stream containing AAC-LC audio and H.264 Main
Profile Level 3.0 video would have a CODECS value of
"mp4a.40.2,avc1.4d401e".
Every EXT-X-STREAM-INF tag SHOULD include a CODECS attribute.
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RESOLUTION
The value is a decimal-resolution describing the optimal pixel
resolution at which to display all the video in the Variant
Stream.
The RESOLUTION attribute is OPTIONAL but is recommended if the
Variant Stream includes video.
FRAME-RATE
The value is a decimal-floating-point describing the maximum frame
rate for all the video in the Variant Stream, rounded to 3 decimal
places.
The FRAME-RATE attribute is OPTIONAL but is recommended if the
Variant Stream includes video. The FRAME-RATE attribute SHOULD be
included if any video in a Variant Stream exceeds 30 frames per
second.
HDCP-LEVEL
The value is an enumerated-string; valid strings are TYPE-0 and
NONE. This attribute is advisory; a value of TYPE-0 indicates
that the Variant Stream could fail to play unless the output is
protected by HDCP Type 0 [HDCP] or equivalent. A value of NONE
indicates that the content does not require output copy
protection.
Encrypted Variant Streams with different HDCP levels SHOULD use
different media encryption keys.
The HDCP-LEVEL attribute is OPTIONAL. It SHOULD be present if any
content in the Variant Stream will fail to play without HDCP.
Clients without output copy protection SHOULD NOT load a Variant
Stream with an HDCP-LEVEL attribute unless its value is NONE.
AUDIO
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
Playlist whose TYPE attribute is AUDIO. It indicates the set of
audio Renditions that SHOULD be used when playing the
presentation. See Section 4.3.4.2.1.
The AUDIO attribute is OPTIONAL.
VIDEO
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The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
Playlist whose TYPE attribute is VIDEO. It indicates the set of
video Renditions that SHOULD be used when playing the
presentation. See Section 4.3.4.2.1.
The VIDEO attribute is OPTIONAL.
SUBTITLES
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
Playlist whose TYPE attribute is SUBTITLES. It indicates the set
of subtitle Renditions that can be used when playing the
presentation. See Section 4.3.4.2.1.
The SUBTITLES attribute is OPTIONAL.
CLOSED-CAPTIONS
The value can be either a quoted-string or an enumerated-string
with the value NONE. If the value is a quoted-string, it MUST
match the value of the GROUP-ID attribute of an EXT-X-MEDIA tag
elsewhere in the Playlist whose TYPE attribute is CLOSED-CAPTIONS,
and indicates the set of closed-caption Renditions that can be
used when playing the presentation. See Section 4.3.4.2.1.
If the value is the enumerated-string value NONE, all EXT-X
-STREAM-INF tags MUST have this attribute with a value of NONE,
indicating that there are no closed captions in any Variant Stream
in the Master Playlist. Having closed captions in one Variant
Stream but not another can trigger playback inconsistencies.
The CLOSED-CAPTIONS attribute is OPTIONAL.
4.3.4.2.1. Alternative Renditions
When an EXT-X-STREAM-INF tag contains an AUDIO, VIDEO, SUBTITLES, or
CLOSED-CAPTIONS attribute, it indicates that alternative Renditions
of the content are available for playback of that Variant Stream.
When defining alternative Renditions, the following constraints MUST
be met to prevent client playback errors:
o All playable combinations of Renditions associated with an EXT-X
-STREAM-INF tag MUST have an aggregate bandwidth less than or
equal to the BANDWIDTH attribute of the EXT-X-STREAM-INF tag.
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o If an EXT-X-STREAM-INF tag contains a RESOLUTION attribute and a
VIDEO attribute, then every alternative video Rendition MUST have
an optimal display resolution matching the value of the RESOLUTION
attribute.
o Every alternative Rendition associated with an EXT-X-STREAM-INF
tag MUST meet the constraints for a Variant Stream described in
Section 6.2.4.
The URI attribute of the EXT-X-MEDIA tag is REQUIRED if the media
type is SUBTITLES, but OPTIONAL if the media type is VIDEO or AUDIO.
If the media type is VIDEO or AUDIO, a missing URI attribute
indicates that the media data for this Rendition is included in the
Media Playlist of any EXT-X-STREAM-INF tag referencing this
EXT-X-MEDIA tag. If the media TYPE is AUDIO and the URI attribute is
missing, clients MUST assume that the audio data for this Rendition
is present in every video Rendition specified by the EXT-X-STREAM-INF
tag.
The URI attribute of the EXT-X-MEDIA tag MUST NOT be included if the
media type is CLOSED-CAPTIONS.
4.3.4.3. EXT-X-I-FRAME-STREAM-INF
The EXT-X-I-FRAME-STREAM-INF tag identifies a Media Playlist file
containing the I-frames of a multimedia presentation. It stands
alone, in that it does not apply to a particular URI in the Master
Playlist. Its format is:
#EXT-X-I-FRAME-STREAM-INF:<attribute-list>
All attributes defined for the EXT-X-STREAM-INF tag (Section 4.3.4.2)
are also defined for the EXT-X-I-FRAME-STREAM-INF tag, except for the
FRAME-RATE, AUDIO, SUBTITLES and CLOSED-CAPTIONS attributes. In
addition, the following attribute is defined:
URI
The value is a quoted-string containing a URI that identifies the
I-frame Media Playlist file. That Playlist file MUST contain an
EXT-X-I-FRAMES-ONLY tag.
Every EXT-X-I-FRAME-STREAM-INF tag MUST include a BANDWIDTH attribute
and a URI attribute.
The provisions in Section 4.3.4.2.1 also apply to EXT-X-I-FRAME-
STREAM-INF tags with a VIDEO attribute.
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A Master Playlist that specifies alternative VIDEO Renditions and
I-frame Playlists SHOULD include an alternative I-frame VIDEO
Rendition for each regular VIDEO Rendition, with the same NAME and
LANGUAGE attributes.
4.3.4.4. EXT-X-SESSION-DATA
The EXT-X-SESSION-DATA tag allows arbitrary session data to be
carried in a Master Playlist.
Its format is:
#EXT-X-SESSION-DATA:<attribute-list>
The following attributes are defined:
DATA-ID
The value of DATA-ID is a quoted-string which identifies that data
value. The DATA-ID SHOULD conform to a reverse DNS naming
convention, such as "com.example.movie.title"; however, there is
no central registration authority, so Playlist authors SHOULD take
care to choose a value which is unlikely to collide with others.
This attribute is REQUIRED.
VALUE
VALUE is a quoted-string. It contains the data identified by
DATA-ID. If the LANGUAGE is specified, VALUE SHOULD contain a
human-readable string written in the specified language.
URI
The value is a quoted-string containing a URI. The resource
identified by the URI MUST be formatted as JSON [RFC7159];
otherwise, clients may fail to interpret the resource.
LANGUAGE
The value is a quoted-string containing a language tag [RFC5646]
that identifies the language of the VALUE. This attribute is
OPTIONAL.
Each EXT-X-SESSION-DATA tag MUST contain either a VALUE or URI
attribute, but not both.
A Playlist MAY contain multiple EXT-X-SESSION-DATA tags with the same
DATA-ID attribute. A Playlist MUST NOT contain more than one EXT-X
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-SESSION-DATA tag with the same DATA-ID attribute and the same
LANGUAGE attribute.
4.3.4.5. EXT-X-SESSION-KEY
The EXT-X-SESSION-KEY tag allows encryption keys from Media Playlists
to be specified in a Master Playlist. This allows the client to
preload these keys without having to read the Media Playlist(s)
first.
Its format is:
#EXT-X-SESSION-KEY:<attribute-list>
All attributes defined for the EXT-X-KEY tag (Section 4.3.2.4) are
also defined for the EXT-X-SESSION-KEY, except that the value of the
METHOD attribute MUST NOT be NONE. If an EXT-X-SESSION-KEY is used,
the values of the METHOD, KEYFORMAT and KEYFORMATVERSIONS attributes
MUST match any EXT-X-KEY with the same URI value.
EXT-X-SESSION-KEY tags SHOULD be added if multiple Variant Streams or
Renditions use the same encryption keys and formats.
The EXT-X-SESSION-KEY tag is optional.
4.3.5. Media or Master Playlist Tags
The tags in this section can appear in either Master Playlists or
Media Playlists. If one of these tags appears in a Master Playlist,
it SHOULD NOT appear in any Media Playlist referenced by that Master
Playlist. A tag that appears in both MUST have the same value;
otherwise, clients SHOULD ignore the value in the Media Playlist(s).
These tags MUST NOT appear more than once in a Playlist. If a tag
appears more than once, clients MUST reject the playlist.
4.3.5.1. EXT-X-INDEPENDENT-SEGMENTS
The EXT-X-INDEPENDENT-SEGMENTS tag indicates that all media samples
in a Media Segment can be decoded without information from other
segments. It applies to every Media Segment in the Playlist.
Its format is:
#EXT-X-INDEPENDENT-SEGMENTS
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If the EXT-X-INDEPENDENT-SEGMENTS tag appears in a Master Playlist,
it applies to every Media Segment in every Media Playlist in the
Master Playlist.
4.3.5.2. EXT-X-START
The EXT-X-START tag indicates a preferred point at which to start
playing a Playlist. By default, clients SHOULD start playback at
this point when beginning a playback session. This tag is OPTIONAL.
Its format is:
#EXT-X-START:<attribute-list>
The following attributes are defined:
TIME-OFFSET
The value of TIME-OFFSET is a signed-decimal-floating-point number
of seconds. A positive number indicates a time offset from the
beginning of the Playlist. A negative number indicates a negative
time offset from the end of the last Media Segment in the
Playlist. This attribute is REQUIRED.
The absolute value of TIME-OFFSET SHOULD NOT be larger than the
Playlist duration. If the absolute value of TIME-OFFSET exceeds
the duration of the Playlist, it indicates either the end of the
Playlist (if positive) or the beginning of the Playlist (if
negative).
If the Playlist does not contain the EXT-X-ENDLIST tag, the TIME-
OFFSET SHOULD NOT be within three target durations of the end of
the Playlist file.
PRECISE
The value is an enumerated-string; valid strings are YES and NO.
If the value is YES, clients SHOULD start playback at the Media
Segment containing the TIME-OFFSET, but SHOULD NOT render media
samples in that segment whose presentation times are prior to the
TIME-OFFSET. If the value is NO, clients SHOULD attempt to render
every media sample in that segment. This attribute is OPTIONAL.
If it is missing, its value should be treated as NO.
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Internet-Draft HTTP Live Streaming September 20165. Key files5.1. Structure of Key files
An EXT-X-KEY tag with a URI attribute identifies a Key file. A Key
file contains a cipher key that can decrypt Media Segments in the
Playlist.
[AES_128] encryption uses 16-octet keys. If the KEYFORMAT of an
EXT-X-KEY tag is "identity", the Key file is a single packed array of
16 octets in binary format.
5.2. IV for [AES_128]
[AES_128] REQUIRES the same 16-octet Initialization Vector (IV) to be
supplied when encrypting and decrypting. Varying this IV increases
the strength of the cipher.
An IV attribute on an EXT-X-KEY tag with a KEYFORMAT of "identity"
specifies an Initialization Vector that can be used when decrypting
Media Segments encrypted with that Key file. IV values for AES-128
are 128-bit numbers.
An EXT-X-KEY tag with a KEYFORMAT of "identity" that does not have an
IV attribute indicates that the Media Sequence Number is to be used
as the IV when decrypting a Media Segment, by putting its big-endian
binary representation into a 16-octet (128-bit) buffer and padding
(on the left) with zeros.
6. Client/Server Responsibilities6.1. Introduction
This section describes how the server generates the Playlist and
Media Segments and how the client should download them for playback.
6.2. Server Responsibilities6.2.1. General Server Responsibilities
The production of the source media is outside the scope of this
document, which simply presumes a source of continuous encoded media
containing the presentation.
The server MUST divide the source media into individual Media
Segments whose duration is less than or equal to a constant target
duration. Segments that are longer than the planned target duration
can trigger playback stalls and other errors.
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The server SHOULD attempt to divide the source media at points that
support effective decode of individual Media Segments, e.g. on packet
and key frame boundaries.
The server MUST create a URI for every Media Segment that enables its
clients to obtain the segment data. If a server supports partial
loading of resources (e.g. via HTTP Range requests), it MAY specify
segments as sub-ranges of larger resources using the EXT-X-BYTERANGE
tag.
Any Media Segment that is specified in a Playlist loaded by a client
MUST be available for immediate download, or playback errors can
occur. Once download starts, its transfer rate SHOULD NOT be
constrained by the segment production process.
HTTP servers SHOULD transfer text files - such as Playlists and
WebVTT segments - using the "gzip" Content-Encoding if the client
indicates that it is prepared to accept it.
The server must create a Media Playlist file (Section 4) that
contains a URI for each Media Segment that the server wishes to make
available, in the order in which they are to be played.
The value of the EXT-X-VERSION tag (Section 4.3.1.2) SHOULD NOT be
greater than what is required for the tags and attributes in the
Playlist - see Section 7.
Changes to the Playlist file MUST be made atomically from the point
of view of the clients, or playback errors MAY occur.
The server MUST NOT change the Media Playlist file, except to:
Append lines to it (Section 6.2.1).
Remove Media Segment URIs from the Playlist in the order that they
appear, along with any tags that apply only to those segments
(Section 6.2.2).
Increment the value of the EXT-X-MEDIA-SEQUENCE or EXT-X
-DISCONTINUITY-SEQUENCE tags (Section 6.2.2).
Add an EXT-X-ENDLIST tag to the Playlist (Section 6.2.1).
A Media Playlist has further constraints on its updates if it
contains an EXT-X-PLAYLIST-TYPE tag. An EXT-X-PLAYLIST-TYPE tag with
a value of VOD indicates that the Playlist file MUST NOT change. An
EXT-X-PLAYLIST-TYPE tag with a value of EVENT indicates that the
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server MUST NOT change or delete any part of the Playlist file; it
MAY append lines to it.
The value of the EXT-X-TARGETDURATION tag in the Media Playlist MUST
NOT change. A typical target duration is 10 seconds.
Playlist changes other than those allowed here can trigger playback
errors and inconsistent client behavior.
Each Media Segment in a Media Playlist has an integer Discontinuity
Sequence Number. The Discontinuity Sequence Number can be used in
addition to the timestamps within the media to synchronize Media
Segments across different Renditions.
A segment's Discontinuity Sequence Number is the value of the EXT-X
-DISCONTINUITY-SEQUENCE tag (or zero if none) plus the number of
EXT-X-DISCONTINUITY tags in the Playlist preceding the URI line of
the segment.
The server MAY associate an absolute date and time with a Media
Segment by applying an EXT-X-PROGRAM-DATE-TIME tag to it. This
defines an informative mapping of the (wall-clock) date and time
specified by the tag to the first media timestamp in the segment,
which may be used as a basis for seeking, for display, or for other
purposes. If a server provides this mapping, it SHOULD apply an
EXT-X-PROGRAM-DATE-TIME tag to every segment that has an
EXT-X-DISCONTINUITY tag applied to it.
The Server MUST NOT add any EXT-X-PROGRAM-DATE-TIME tag to a Playlist
that would cause the mapping between program date and Media Segment
to become ambiguous.
The server MUST NOT remove an EXT-X-DATERANGE tag from a Playlist if
any date in the range maps to a Media Segment in the Playlist.
The server MUST NOT reuse the ID attribute value of an
EXT-X-DATERANGE tag for any new Date Range in the same Playlist.
Once the Following Range of a Date Range with an END-ON-NEXT=YES
attribute is added to a Playlist, the Server MUST NOT subsequently
add a Date Range with the same CLASS attribute whose START-DATE is
between that of the END-ON-NEXT=YES range and its Following Range.
For Date Ranges with a PLANNED-DURATION attribute, the Server SHOULD
signal the actual end of the range once it has been established. It
can do so by adding another EXT-X-DATERANGE tag with the same ID
attribute value and either a DURATION or an END-DATE attribute or, if
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the Date Range has an END-ON-NEXT=YES attribute, by adding a
Following Range.
If the Media Playlist contains the final Media Segment of the
presentation then the Playlist file MUST contain the EXT-X-ENDLIST
tag; this allows clients to minimize unproductive Playlist reloads.
If a Media Playlist does not contain the EXT-X-ENDLIST tag, the
server MUST make a new version of the Playlist file available that
contains at least one new Media Segment. It MUST be made available
relative to the time that the previous version of the Playlist file
was made available: no earlier than one-half the target duration
after that time, and no later than 1.5 times the target duration
after that time. This allows clients to utilize the network
efficiently.
If the server wishes to remove an entire presentation, it SHOULD
provide a clear indication to clients that the Playlist file is no
longer available (e.g. with an HTTP 404 or 410 response). It MUST
ensure that all Media Segments in the Playlist file remain available
to clients for at least the duration of the Playlist file at the time
of removal to prevent interruption of in-progress playback.
6.2.2. Live Playlists
The server MAY limit the availability of Media Segments by removing
Media Segments from the Playlist file (Section 6.2.1). If Media
Segments are to be removed, the Playlist file MUST contain an EXT-X
-MEDIA-SEQUENCE tag. Its value MUST be incremented by 1 for every
Media Segment that is removed from the Playlist file; it MUST NOT
decrease or wrap. Clients can malfunction if each Media Segment does
not have a consistent, unique Media Sequence Number.
Media Segments MUST be removed from the Playlist file in the order
that they appear in the Playlist; otherwise, client playback can
malfunction.
The server MUST NOT remove a Media Segment from a Playlist file
without an EXT-X-ENDLIST tag if that would produce a Playlist whose
duration is less than three times the target duration. Doing so can
trigger playback stalls.
When the server removes a Media Segment URI from the Playlist, the
corresponding Media Segment MUST remain available to clients for a
period of time equal to the duration of the segment plus the duration
of the longest Playlist file distributed by the server containing
that segment. Removing a Media Segment earlier than that can
interrupt in-progress playback.
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If the server wishes to remove segments from a Media Playlist
containing an EXT-X-DISCONTINUITY tag, the Media Playlist MUST
contain an EXT-X-DISCONTINUITY-SEQUENCE tag. Without the EXT-X
-DISCONTINUITY-SEQUENCE tag, it can be impossible for a client to
locate corresponding segments between Renditions.
If the server removes an EXT-X-DISCONTINUITY tag from the Media
Playlist, it MUST increment the value of the EXT-X-DISCONTINUITY-
SEQUENCE tag so that the Discontinuity Sequence Numbers of the
segments still in the Media Playlist remain unchanged. The value of
the EXT-X-DISCONTINUITY-SEQUENCE tag MUST NOT decrease or wrap.
Clients can malfunction if each Media Segment does not have a
consistent Discontinuity Sequence Number.
If a server plans to remove a Media Segment after it is delivered to
clients over HTTP, it SHOULD ensure that the HTTP response contains
an Expires header that reflects the planned time-to-live.
A Live Playlist MUST NOT contain the EXT-X-PLAYLIST-TYPE tag, as no
value of that tag allows Media Segments to be removed.
6.2.3. Encrypting Media Segments
Media Segments MAY be encrypted. Every encrypted Media Segment MUST
have an EXT-X-KEY tag (Section 4.3.2.4) applied to it with a URI that
the client can use to obtain a Key file (Section 5) containing the
decryption key.
A Media Segment can only be encrypted with one encryption METHOD,
using one encryption key and IV. However, a server MAY offer
multiple ways to retrieve that key by providing multiple EXT-X-KEY
tags, each with a different KEYFORMAT attribute value.
The server MAY set the HTTP Expires header in the key response to
indicate the duration for which the key can be cached.
If an encrypted Media Segment is followed by one or more unencrypted
Media Segments in the Playlist, the unencrypted Media Segments MUST
have an EXT-X-KEY tag whose METHOD is NONE applied to them.
Otherwise, the client will misinterpret those segments as encrypted.
If the encryption METHOD is AES-128 and the Playlist does not contain
the EXT-X-I-FRAMES-ONLY tag, AES encryption as described in
Section 4.3.2.4 SHALL be applied to individual Media Segments.
If the encryption METHOD is AES-128 and the Playlist contains an
EXT-X-I-FRAMES-ONLY tag, the entire resource MUST be encrypted using
AES-128 CBC with PKCS7 padding [RFC5652]. Encryption MAY be
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restarted on 16-byte block boundaries, unless the first block
contains an I-frame. The IV used for encryption MUST be either the
Media Sequence Number of the Media Segment or the value of the IV
attribute of the EXT-X-KEY tag, as described in Section 5.2. These
constraints allow a client to load and decrypt individual I-frames
specified as sub-ranges of regular encrypted Media Segments, and
their Media Initialization Sections.
If the encryption METHOD is SAMPLE-AES, media samples MAY be
encrypted prior to encapsulation in a Media Segment.
The server MUST NOT remove an EXT-X-KEY tag from the Playlist file if
it applies to any Media Segment in the Playlist file, or clients who
subsequently load that Playlist will be unable to decrypt those Media
Segments.
6.2.4. Providing Variant Streams
A server MAY offer multiple Media Playlist files to provide different
encodings of the same presentation. If it does so it SHOULD provide
a Master Playlist file that lists each Variant Stream to allow
clients to switch between encodings dynamically.
Master Playlists describe regular Variant Streams with EXT-X-STREAM-
INF tags and I-frame Variant Streams with EXT-X-I-FRAME-STREAM-INF
tags.
If an EXT-X-STREAM-INF tag or EXT-X-I-FRAME-STREAM-INF tag contains
the CODECS attribute, the attribute value MUST include every media
format [RFC6381] present in any Media Segment in any of the
Renditions specified by the Variant Stream.
The server MUST meet the following constraints when producing Variant
Streams in order to allow clients to switch between them seamlessly:
Each Variant Stream MUST present the same content.
Matching content in Variant Streams MUST have matching timestamps.
This allows clients to synchronize the media.
Matching content in Variant Streams MUST have matching
Discontinuity Sequence Numbers - see Section 4.3.3.3.
Each Media Playlist in each Variant Stream MUST have the same
target duration. The only exceptions are SUBTITLES Renditions and
Media Playlists containing an EXT-X-I-FRAMES-ONLY tag, which MAY
have different target durations if they have an EXT-X-PLAYLIST-
TYPE of VOD.
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Content that appears in a Media Playlist of one Variant Stream but
not in another MUST appear either at the beginning or at the end
of the Media Playlist file and MUST NOT be longer than the target
duration.
If any Media Playlists have an EXT-X-PLAYLIST-TYPE tag, all Media
Playlists MUST have the EXT-X-PLAYLIST-TYPE tag with the same
value.
If the Playlist contains an EXT-X-PLAYLIST-TYPE tag with the value
of VOD, the first segment of every Media Playlist in every Variant
Stream MUST start at the same media timestamp.
If any Media Playlist in a Master Playlist contains an EXT-X
-PROGRAM-DATE-TIME tag, then all Media Playlists in that Master
Playlist MUST contain EXT-X-PROGRAM-DATE-TIME tags with consistent
mappings of date and time to media timestamps.
Each Variant Stream MUST contain the same set of Date Ranges, each
one identified by EXT-X-DATERANGE tag(s) with the same ID
attribute value and containing the same set of attributes / value
pairs.
In addition, for broadest compatibility, Variant Streams SHOULD
contain the same encoded audio bitstream. This allows clients to
switch between Variant Streams without audible glitching.
The rules for Variant Streams also apply to alternative Renditions -
see Section 4.3.4.2.1.
6.3. Client Responsibilities6.3.1. General Client Responsibilities
How the client obtains the URI to the Playlist file is outside the
scope of this document; it is presumed to have done so.
The client obtains the Playlist file from the URI. If the Playlist
file so obtained is a Master Playlist, the client can select a
Variant Stream to load from the Master Playlist.
Clients MUST ensure that loaded Playlists comply with Section 4 and
that the EXT-X-VERSION tag, if present, specifies a protocol version
supported by the client; if either check fails, the client MUST NOT
attempt to use the Playlist, or unintended behavior could occur.
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If any URI element in a Playlist contains an URI scheme that the
client cannot handle, the client MUST stop playback. All clients
MUST support HTTP schemes.
To support forward compatibility, when parsing Playlists, Clients
MUST:
o ignore any unrecognized tags.
o ignore any Attribute/value pair with an unrecognized
AttributeName.
o ignore any tag containing an attribute/value pair of type
enumerated-string whose AttributeName is recognized but whose
AttributeValue is not recognized, unless the definition of the
attribute says otherwise.
Algorithms used by the client to switch between Variant Streams are
beyond the scope of this document.
6.3.2. Loading the Media Playlist file
Every time a Media Playlist is loaded or reloaded from a Playlist
URI, the client MUST determine the next Media Segment to load, as
described in Section 6.3.5, if it intends to play the presentation
normally (i.e., in playlist order at the nominal playback rate).
If the Media Playlist contains the EXT-X-MEDIA-SEQUENCE tag, the
client SHOULD assume that each Media Segment in it will become
unavailable at the time that the Playlist file was loaded plus the
duration of the Playlist file.
A client MAY use the segment Media Sequence Number to track the
location of a Media Segment within a Playlist when the Playlist is
reloaded.
A client MUST NOT assume that segments with the same Media Sequence
Number in different Variant Streams or Renditions have the same
position in the presentation; Playlists MAY have independent Media
Sequence Numbers. Instead, a client MUST use the relative position
of each segment on the Playlist timeline and its Discontinuity
Sequence Number to locate corresponding segments.
A client MUST load the Media Playlist file of every Rendition
selected for playback in order to locate the media specific to that
Rendition. But, to prevent unnecessary load on the server, it SHOULD
NOT load the Playlist file of any other Rendition.
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For some Variant Streams, it is possible to select Renditions that do
not include the Rendition specified by the EXT-X-STREAM-INF tag. As
noted above, the client SHOULD NOT load that Rendition in those
cases.
6.3.3. Playing the Media Playlist file
The client SHALL choose which Media Segment to play first from the
Media Playlist when playback starts. If the EXT-X-ENDLIST tag is not
present and the client intends to play the media normally, the client
SHOULD NOT choose a segment which starts less than three target
durations from the end of the Playlist file. Doing so can trigger
playback stalls.
Normal playback can be achieved by playing the Media Segments in the
order that they appear in the Playlist. The client MAY present the
available media in any way it wishes, including normal playback,
random access, and trick modes.
The encoding parameters for samples in a Media Segment and across
multiple Media Segments in a Media Playlist SHOULD remain consistent.
However, clients SHOULD deal with encoding changes as they are
encountered, for example by scaling video content to accommodate a
resolution change. If the Variant Stream includes a RESOLUTION
attribute, clients SHOULD display all video within a rectangle with
the same proportions as that resolution.
Clients SHOULD be prepared to handle multiple tracks of a particular
type (e.g. audio or video). A client with no other preference SHOULD
choose the track with the lowest numerical track identifier that it
can play.
Clients SHOULD ignore private streams inside Transport Streams that
they do not recognize. Private streams can be used to support
different devices with the same stream, although stream authors
SHOULD be sensitive to the additional network load that this imposes.
The client MUST be prepared to reset its parser(s) and decoder(s)
before playing a Media Segment that has an EXT-X-DISCONTINUITY tag
applied to it, otherwise playback errors can occur.
The client SHOULD attempt to load Media Segments in advance of when
they will be required for uninterrupted playback to compensate for
temporary variations in latency and throughput.
The client MAY use the value of the EXT-X-PROGRAM-DATE-TIME tag to
display the program origination time to the user. If the value
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includes time zone information, the client SHALL take it into
account; if it does not the client MAY assume the time to be local.
Note that dates in Playlists can refer to when the content was
produced (or to other times), which have no relation to the time of
playback.
If the first EXT-X-PROGRAM-DATE-TIME tag in a Playlist appears after
one or more media segment URIs, the client SHOULD extrapolate
backward from that tag (using EXTINF durations and/or media
timestamps) to associate dates with those segments. To associate a
date with any other media segment that does not have an EXT-X
-PROGRAM-DATE-TIME tag applied to it directly , the client SHOULD
extrapolate forward from the last EXT-X-PROGRAM-DATE-TIME tag
appearing before that segment in the Playlist.
6.3.4. Reloading the Media Playlist file
The client MUST periodically reload a Media Playlist file to learn
what media is currently available, unless it contains an EXT-X
-PLAYLIST-TYPE tag with a value of VOD, or a value of EVENT and the
EXT-X-ENDLIST tag is also present.
However the client MUST NOT attempt to reload the Playlist file more
frequently than specified by this section, in order to limit the
collective load on the server.
When a client loads a Playlist file for the first time or reloads a
Playlist file and finds that it has changed since the last time it
was loaded, the client MUST wait for at least the target duration
before attempting to reload the Playlist file again, measured from
the last time the client began loading the Playlist file.
If the client reloads a Playlist file and finds that it has not
changed then it MUST wait for a period of one-half the target
duration before retrying.
After reloading a Media Playlist, the client SHOULD verify that each
Media Segment in it has the same URI (and byte range, if specified)
as the Media Segment with the same Media Sequence Number in the
previous Media Playlist. It SHOULD halt playback if it does not, as
this normally indicates a server error.
In order to reduce server load, the client SHOULD NOT reload the
Playlist files of Variant Streams or alternate Renditions that are
not currently being played. If it decides to switch playback to a
different Variant Stream, it SHOULD stop reloading the Playlist of
the old Variant Stream and begin loading the Playlist of the new
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Variant Stream. It can use the EXTINF durations and the constraints
in Section 6.2.4 to determine the approximate location of
corresponding media. Once media from the new Variant Stream has been
loaded, the timestamps in the Media Segments can be used to
synchronize the old and new timelines precisely.
A client MUST NOT attempt to use the Media Sequence Number to
synchronize between streams - see Section 6.3.2.
6.3.5. Determining the next segment to load
The client MUST examine the Media Playlist file every time it is
loaded or reloaded to determine the next Media Segment to load, as
the set of available media MAY have changed.
The first segment to load is generally the segment that the client
has chosen to play first - see Section 6.3.3.
In order to play the presentation normally, the next Media Segment to
load is the one with the lowest Media Sequence Number that is greater
than the Media Sequence Number of the last Media Segment loaded.
6.3.6. Decrypting encrypted Media Segments
If a Media Playlist file contains an EXT-X-KEY tag that specifies a
Key file URI, the client can obtain that Key file and use the key
inside it to decrypt all Media Segments to which that EXT-X-KEY tag
applies.
A client MUST ignore any EXT-X-KEY tag with an unsupported or
unrecognized KEYFORMAT attribute, to allow for cross-device
addressibility. If the Playlist contains a Media Segment to which
only EXT-X-KEY tags with unrecognized or unsupported KEYFORMAT
attributes are applied, playback SHOULD fail.
A client MUST NOT attempt to decrypt any segments whose EXT-X-KEY tag
has a METHOD attribute that it does not recognize.
If the encryption METHOD is AES-128, AES-128 CBC decryption SHALL be
applied to individual Media Segments, whose encryption format is
described in Section 4.3.2.4.
If the encryption METHOD is AES-128 and the Media Segment is part of
an I-frame playlist (Section 4.3.3.6) and it has an EXT-X-BYTERANGE
tag applied to it, special care needs to be taken in loading and
decrypting the segment, because the resource identified by the URI is
encrypted in 16-byte blocks from the start of the resource.
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The decrypted I-frame can be recovered by first widening its byte
range, as specified by the EXT-X-BYTERANGE tag, so that it starts and
ends on 16-byte boundaries from the start of the resource.
Next, the byte range is widened further to include a 16-byte block at
the beginning of the range. This 16-byte block allows the correct IV
for the following block to be calculated.
The widened byte range can then be loaded and decrypted with AES-128
CBC using an arbitrary IV. The number of bytes added to the
beginning and the end of the original byte range are discarded from
the decrypted bytes; what remains is the decrypted I-frame.
If the encryption METHOD is SAMPLE-AES, AES-128 decryption SHALL be
applied to encrypted media samples within the Media Segment.
An EXT-X-KEY tag with a METHOD of NONE indicates that the Media
Segments it applies to are not encrypted.
7. Protocol version compatibility
Protocol compatibility is specified by the EXT-X-VERSION tag. A
Playlist that contains tags or attributes that are not compatible
with protocol version 1 MUST include an EXT-X-VERSION tag.
A client MUST NOT attempt playback if it does not support the
protocol version specified by the EXT-X-VERSION tag, or unintended
behavior could occur.
A Media Playlist MUST indicate a EXT-X-VERSION of 2 or higher if it
contains:
o The IV attribute of the EXT-X-KEY tag.
A Media Playlist MUST indicate a EXT-X-VERSION of 3 or higher if it
contains:
o Floating-point EXTINF duration values.
A Media Playlist MUST indicate a EXT-X-VERSION of 4 or higher if it
contains:
o The EXT-X-BYTERANGE tag.
o The EXT-X-I-FRAMES-ONLY tag.
A Media Playlist MUST indicate a EXT-X-VERSION of 5 or higher if it
contains:
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o The KEYFORMAT and KEYFORMATVERSIONS attributes of the EXT-X-KEY
tag.
o The EXT-X-MAP tag.
A Media Playlist MUST indicate a EXT-X-VERSION of 6 or higher if it
contains:
o The EXT-X-MAP tag in a Media Playlist that does not contain
EXT-X-I-FRAMES-ONLY.
A Master Playlist MUST indicate a EXT-X-VERSION of 7 or higher if it
contains:
o "SERVICE" values for the INSTREAM-ID attribute of the EXT-X-MEDIA
tag.
The EXT-X-MEDIA tag and the AUDIO, VIDEO and SUBTITLES attributes of
the EXT-X-STREAM-INF tag are backward compatible to protocol version
1, but playback on older clients may not be desirable. A server MAY
consider indicating a EXT-X-VERSION of 4 or higher in the Master
Playlist but is not required to do so.
The PROGRAM-ID attribute of the EXT-X-STREAM-INF and the EXT-X-I
-FRAME-STREAM-INF tags was removed in protocol version 6.
The EXT-X-ALLOW-CACHE tag was removed in protocol version 7.
8. Playlist Examples8.1. Simple Media Playlist
#EXTM3U
#EXT-X-TARGETDURATION:10
#EXTINF:9.009,
http://media.example.com/first.ts
#EXTINF:9.009,
http://media.example.com/second.ts
#EXTINF:3.003,
http://media.example.com/third.ts
#EXT-X-ENDLIST
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#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1280000
low/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=86000,URI="low/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=2560000
mid/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=150000,URI="mid/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=7680000
hi/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=550000,URI="hi/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
audio-only.m3u8
8.6. Master Playlist with Alternative audio
In this example, the CODECS attributes have been condensed for space.
A '\' is used to indicate that the tag continues on the following
line with whitespace removed:
#EXTM3U
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="English", \
DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="en", \
URI="main/english-audio.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Deutsch", \
DEFAULT=NO,AUTOSELECT=YES,LANGUAGE="de", \
URI="main/german-audio.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Commentary", \
DEFAULT=NO,AUTOSELECT=NO,LANGUAGE="en", \
URI="commentary/audio-only.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",AUDIO="aac"
low/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",AUDIO="aac"
mid/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",AUDIO="aac"
hi/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5",AUDIO="aac"
main/english-audio.m3u8
8.7. Master Playlist with Alternative video
This example shows 3 different video Renditions (Main, Centerfield
and Dugout), and 3 different Variant Streams (low, mid and high). In
this example, clients that did not support the EXT-X-MEDIA tag and
the VIDEO attribute of the EXT-X-STREAM-INF tag would only be able to
play the video Rendition "Main".
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Since the EXT-X-STREAM-INF tag has no AUDIO attribute, all video
Renditions would be required to contain the audio.
In this example, the CODECS attributes have been condensed for space.
A '\' is used to indicate that the tag continues on the following
line with whitespace removed:
#EXTM3U
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Main", \
DEFAULT=YES,URI="low/main/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Centerfield", \
DEFAULT=NO,URI="low/centerfield/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Dugout", \
DEFAULT=NO,URI="low/dugout/audio-video.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",VIDEO="low"
low/main/audio-video.m3u8
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Main", \
DEFAULT=YES,URI="mid/main/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Centerfield", \
DEFAULT=NO,URI="mid/centerfield/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Dugout", \
DEFAULT=NO,URI="mid/dugout/audio-video.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",VIDEO="mid"
mid/main/audio-video.m3u8
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Main", \
DEFAULT=YES,URI="hi/main/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Centerfield", \
DEFAULT=NO,URI="hi/centerfield/audio-video.m3u8"
#EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Dugout", \
DEFAULT=NO,URI="hi/dugout/audio-video.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",VIDEO="hi"
hi/main/audio-video.m3u8
8.8. Session Data in a Master Playlist
In this example, only the EXT-X-SESSION-DATA is shown:
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Required parameters: (none)
Optional parameters: (none)
Encoding considerations: encoded as UTF-8 text. See Section 4 for
more information.
Security considerations: See Section 11.
Compression: this media type does not employ compression.
Interoperability considerations: There are no byte-ordering issues,
since files are 7- or 8-bit text. Applications could encounter
unrecognized tags, which SHOULD be ignored.
Published specification: see Section 4.
Applications that use this media type: Multimedia applications such
as the iPhone media player in iOS 3.0 and later and QuickTime Player
in Mac OS X version 10.6 and later.
Additional information: files begin with the magic number #EXTM3U.
Filenames normally end with .m3u8 or .m3u (see Section 4). No
Macintosh file type codes have been registered.
Person & email address to contact for further information: David
Singer, singer AT apple.com.
Intended usage: LIMITED USE
Restrictions on usage: (none)
Author: Roger Pantos
Change Controller: David Singer
11. Security Considerations
Since the protocol generally uses HTTP to transfer data, most of the
same security considerations apply. See section 15 of HTTP
[RFC7230].
Media file parsers are typically subject to "fuzzing" attacks.
Implementors SHOULD pay particular attention to code that will parse
data received from a server and ensure that all possible inputs are
handled correctly.
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Playlist files contain URIs, which clients will use to make network
requests of arbitrary entities. Clients SHOULD range-check responses
to prevent buffer overflows. See also the Security Considerations
section of Uniform Resource Identifier (URI): Generic Syntax
[RFC3986].
Clients SHOULD limit each playback session to a reasonable number of
concurrent downloads (e.g. 4) to avoid contributing to denial-of-
service attacks.
HTTP requests often include session state ("cookies"), which may
contain private user data. Implementations MUST follow cookie
restriction and expiry rules specified by HTTP State Management
Mechanism [RFC6265] to protect themselves from attack. See also the
Security Considerations section of that document, and Use of HTTP
State Management [RFC2964].
Encryption keys are specified by URI. The delivery of these keys
SHOULD be secured by a mechanism such as HTTP Over TLS [RFC2818]
(formerly SSL) in conjunction with a secure realm or a session token.
12. References12.1. Normative References
[AC_3] Advanced Television Systems Committee, "ATSC Standard:
A/52:2010: Digital Audio Compression (AC-3) (E-AC-3)
Standard", November 2010, <http://atsc.org/wp-content/uploads/2015/03/A52-201212-17.pdf>.
[AES_128] U.S. Department of Commerce/National Institute of
Standards and Technology, "Advanced Encryption Standard
(AES), FIPS PUB 197", November 2001, <http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf>.
[CEA608] Consumer Electronics Association, "CEA-608-E: Line 21 Data
Services", April 2008, <http://www.ce.org/Standards/Standard-Listings/R4-3-Television-Data-Systems-Subcommittee/Line-21-Data-Service.aspx>.
[CEA708] Consumer Electronics Association, "CEA-708-E (ANSI):
Digital Television (DTV) Closed Captioning", August 2013,
<http://www.ce.org/Standards/Standard-Listings/R4-3-Television-Data-Systems-Subcommittee/CEA-708-D.aspx>.
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William May, Jr.
Major League Baseball Advanced Media
New York, New York
United States
Email: bill.may@mlb.com
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